The present invention relates to an automatic plant for thermal treatments of metals, in particular steel metals.
It is known that plants having a batch operation for thermal treatments of steel metals in a controlled atmosphere comprise a varying number of work stations among which, in addition to a series of stations or stands for loading-unloading charge-holding baskets, provision is made for one or more reheating and/or high-temperature thermochemical-treatment chambers or furnaces, one or more tempering and/or low-temperature thermochemical-treatment chambers or furnaces, one or more cooling or hardening stations, and one or more washing or rinsing stations.
Charge-holding baskets extending both horizontally and vertically are currently transported in plants of known type provided with work chambers having the conformation of a room, i.e. in which the loading and unloading opening is positioned at the lower part of same, by transfer tables sliding on tracks or by sliding grid conveyors at the outside and inside of tightly sealed chambers in which all work stations requiring to operate in a controlled atmosphere are housed.
The known art briefly described above however has many limits and drawbacks.
This technique in fact highlights a great rigidity in the range of the treatments It offers because the necessarily limited number of work stations susceptible of alignment within a Lightly sealed chamber needs important and expensive plant modifications and often special dedicated plants for being increased and adapted to the new operating requirements.
In addition, the controlled-atmosphere volumes of the spaces necessary for charge transferring are very extended even for few work stations, and therefore consumption of technical gases that need to be present in these spaces for supply of the controlled atmosphere of different types is also very important.
It is to be added that known plants, in which actuation of the charge-holding baskets takes place by sliding, reduce the possibility of filling these structures with important weights due to deformation and wear of the structures themselves and the related sliding guides. Also due to the fact that the actuation means of the charge-holding baskets is located at areas subjected to critical temperatures and temperature changes, strong stresses occur that limit the maximum amount of the loads that can be carried.
Finally, arrangement of the stations within the tightly sealed chambers makes it difficult to accede thereto for both ordinary and extraordinary servicing interventions.
Beside the above described plants, also known are plants of vertical extension in which furnaces hanging from an overhead rail slide and get aligned at the various work stations. In these plants elevator-provided loading-unloading apparatuses and hooking-releasing devices positioned on each of the lower stations are contemplated.
This second plant typology clearly shows a great construction complexity, as it is necessary to handle a plurality of furnaces in order to maximize the operating flexibility of the plant. In addition, in this case too, the actuation means operating within each furnace undergoes important thermal stresses limiting the maximum transportable loads. On the other hand, it is impossible to think of working with too heavy loads since overhead furnaces cannot be of too big sizes as they must be conveniently supported and handled and thermally insulated in an efficient manner.
As regards safety too, it is apparent that the presence of overhead moving furnaces is not a particularly desirable situation.